1. Field of the Invention
The present invention relates to a channel state information compressing apparatus and a corresponding method, a channel state information expanding apparatus and a corresponding method, computer programs, a receiver, and a transmitter.
Priority is claimed on Japanese Patent Application No. 2009-278481, filed Dec. 8, 2009, the contents of which are incorporated herein by reference.
2. Description of the Related Art
For advanced wireless communication system, employment of a MIMO (multiple input and multiple output) system has been examined. In the MIMO system, a transmitter precodes transmitted data based on CSI (channel state information) which indicates the state of a signal transmission path (i.e., communication channel), which can improve the efficiency in frequency usage in comparison with a case of performing no precoding (see, for example, M. Vu and A. Paulraj, “MIMO Wireless Linear Precoding”, IEEE Signal Processing Magazine, pp. 86-105, September, 2007).
Additionally, when employing an FDD (frequency division duplex) method, the channel state information is generally obtained by a receiver. As a method of precoding transmitted data based on the channel state information, the following two methods are known (see, for example, 3GPP TS 36.211 V.8.7.0, pp. 53-54, May 2009):
(i) A receiver obtains a channel response matrix, and sends it to a transmitter. The transmitter then performs precoding in accordance with the channel response matrix.
(ii) A transmitter and a receiver commonly have a codebook which includes index numbers of a plurality of precoders. The receiver obtains a channel response matrix, and sends the index number of a precoder corresponding to the channel response matrix to the transmitter. The transmitter uses a precoder which has the relevant index number.
In the above method (i), the transmitter can perform precoding by using the channel response matrix obtained by the receiver. However, the amount of information of the channel response matrix sent from the receiver to the transmitter is large, which requires a large amount of wireless resources used for transmitting the information.
In the above method (ii), the amount of information sent from the receiver to the transmitter can be reduced. However, the number of precoder types, which can be recorded in the codebook, is limited. Therefore, if there is no precoder suitable for the channel response matrix obtained by the receiver, the effect of precoding is degraded.